This invention relates to a sheet unloading device for use in a duplicating machine or the like wherein sheets are delivered seriatim at the exit end of the machine.
Printing or duplicating machines, such as rotary offset lithographic duplicating machines, normally are provided with some form of sheet receiving means at the exit end of the machine for stacking copy sheets issuing from the machine. Conventionally, the sheet receiving means comprises a receiving tray for receiving and stacking the sheets. The sheets normally fall by gravity and come to rest onto the top of a stack in the tray. Periodically, or when the tray is full, the stack of sheets is removed from the tray by the machine operator. This normally is done simply by grasping the stack and lifting the stack out of the tray. Aside from unloading the tray, the machine operator may wish to remove one or more copy sheets at a time while the machine is operating to inspect the quality of the duplicated copies. The removal of the stack of sheets or the selected inspection of a single copy usually can be performed by a skilled operator while the machine is operating at relatively slow speeds. However, such operations are extremely difficult, if at all possible, at higher machine speeds such as on the order of 8,000 to 15,000 impressions per hour (IPH). A target of some such machines is to reach 20,000 impressions per hour. At the higher speeds, the slightest disturbance of a single sheet normally results in sheet jamming. The present invention can be used at all speed levels and is particularly useful with machines operating at the higher speeds.
In addition, larger or longer sizes are more difficult to unload because of the smaller gap or time interval between the trailing end of one sheet and the leading of a succeeding sheet being deposited in the tray. Also, the weight of larger sheets increases the difficulty of unloading the tray. Accordingly, the usual procedure for performing such operations as unloading or sheet inspection at high machine speeds is to stop the feeding of sheets to the machine or to shut down the machine completely.
There is a need for a device which permits unloading of the receiving tray while the machine is running at high speeds without interruption of the sheet feeding operation or stopping the machine as is normally required by prior devices. Such a device would greatly increase production because continuous unloading permits an operator to complete a full feeder load without stopping to unload the receiving tray. Continuous unloading also would permit an operator to inspect the quality of the duplicated copies as well as to perform other functions, such as preparing for the next color run on the previously duplicated copies, turning the stock over for back-up printing, packaging the stock for delivery or moving the stock to a subsequent operation. All of these extraneous functions heretofore had to be performed during machine shut-down.
The invention is directed to a device for unloading sheets from the receiving tray while the machine continues to operate at high speeds and while sheets are continuously being delivered to the receiving tray.